Hard anodizing film is the most characteristic of many anodic oxidation films of aluminum and its alloys, and its main characteristics are as follows.
(1) the appearance of the film. The appearance of the film appears gray, brown and black with the difference of substrate material composition and process conditions. Under the rated condition, with the decrease of electrolyte temperature, the film thickness increases and the color deepens. Using the change of this process condition, the oxide film with different thickness and color can be obtained in a certain range.
(2) film thickness. The thickness of the film is related to the purity of the substrate and the process conditions. The higher the purity of the substrate, the lower the temperature of the electrolyte under the rated conditions, so that a thicker oxide film can be obtained. The maximum thickness of the oxide film can reach 150-250μm.
(3) hardness of the film. The hardness of the oxide film is higher, but the hardness of the film varies greatly with the purity of the substrate. The hardness of the film on pure aluminum can reach 1200% 1500, while the hardness of the film on aluminum alloy is significantly reduced, usually only about HV400.
(4) film lubricity. The micropores of the film can adsorb lubricants, which is beneficial to improve the lubricity and wear resistance.
(5) corrosion resistance of the film. The film has high corrosion resistance, does not suffer corrosion for a long time under industrial atmospheric conditions, and also has excellent corrosion resistance in marine climate, such as sealing treatment, its corrosion resistance is better.
(6) heat resistance of the film. The melting point of the oxide film can reach 2050 ℃, and its thermal conductivity is as low as 0.67W/ (cm ℃). It is an excellent heat resistant material.
(7) film insulation. The resistance of the film is large, the thickness of the film is 10 μ m, and it can withstand the voltage of more than 2000V.
(8) membrane binding force. The combination of the film layer and its substrate is firm and reliable.
Because aluminum and its alloy parts have the above excellent characteristics after hard anodizing treatment, they are widely used, especially in the fields of national defense industry, aviation, aerospace and so on. In these areas, the manufacture of heat-resistant, wear-resistant, insulated aluminum parts, such as pistons, cylinders, bearings, hydraulic equipment, water, electrical equipment in the impeller, shock absorbers and other parts. This process is often used to improve the original performance of these parts.